CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CD-adapco

High residuals

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   November 25, 2008, 13:26
Default High residuals
  #1
ecram
Guest
 
Posts: n/a
Hello, I have a new question for You, in my simulation of wing in free flux, the residual are high but the result in terms of Cl and Cp is good which it is the reason?

TankU
  Reply With Quote

Old   November 25, 2008, 22:17
Default Re: High residuals
  #2
no one
Guest
 
Posts: n/a
The magnitude of the residuals is not important, they are pretty arbitrary. I think Star-CD and Star-CCM+ normalize your residuals by the largest change in any cell from iteration 0 to iteration 1. If the initial conditions were very close to the solution, then your residuals will be normalized by a very small number, making the residuals high. The thing to look out for is increasing or oscillating residuals that could indicated mesh or setup problems. Monitoring values like Cp and Cl as you have done is a much better gauge of convergence. Residuals are a better indicator of mesh quality than convergence.
  Reply With Quote

Old   November 26, 2008, 03:43
Default Re: High residuals
  #3
ecram
Guest
 
Posts: n/a
Thank you very much hour I am most calmer

  Reply With Quote

Old   November 26, 2008, 08:19
Default Re: High residuals
  #4
James
Guest
 
Posts: n/a
At least in 3.26 you can turn ANORM on.

This turns the residual methodology back to the former physics based system, used before they decided that they needed to be like Fluent.

For most of the variables this ends up being the sum of all fluxes through the cell walls normalized by the inlet flux.

The absolute value is related to the inlet flux to volume of the model, but at least it means something physical.

I believe they changed because Fluent was 'easier' and 'faster' to converge. Since you have no real idea what these numbers mean if the number was low then you can pretend that it is converged if it asymptotes.

It is somewhat strange that if you have a bad initial guess you can converge faster (fewer iterations) than if you mapped a full solution. In the first case the initial residuals are very poor and can be reduced fast, in the second case you may be very near convergence and thus they should not change much.

  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Residuals converged but high Gilles CFX 2 September 30, 2008 19:05
help high initial residuals Aly FLUENT 0 October 11, 2007 09:04
Help HIGH RESIDUALS Aly NUMECA 0 October 11, 2007 08:57
residuals Karl CFX 2 June 24, 2003 23:13
residuals andrea CD-adapco 0 March 6, 2002 09:41


All times are GMT -4. The time now is 12:30.